The hydraulically operated rotary machine or hydraulic motor with a nutating bevel gear transmission train therein is well known in the art and is advantageous over other types of hydraulic motors of comparable size in that low speed and high torque power may be derived and in that it may be readily converted into a hydraulic motor with a brake when a brake means is incorporated to retard and arrest the rotation of a shaft rotated at high speed.
However, it has also some disadvantages as will be described below.
(1) The bevel gear as a nutating member is rigidly and unrotatably carried by a crankshaft so that the dimensional accuracy of the crankshaft both in fabrication and assembly and the deflection thereof under load greatly affects not only the valve timing for for reciprocating pistons in a predetermined timed sequence, but the accuracy in meshing between the mating bevel gears. To overcome these problems, the component parts must be assembled with a higher degree of accuracy and the sub-assembly or the assembly must be adjusted also to a higher degree of accuracy. Thus the assembly requires a long time to manufacture.
(2) It is preferable that either the shaft or the casing is rotatable as needs demand, but the conventional hydraulic motors of the type described cannot rotate their casings while maintaining the shafts stationary.
(3) The space available for bearings journalling the output shaft is limited so that the capacity of the bearings and their mounting methods are limited. As a result, the load carried by the output shaft becomes inevitably low. Furthermore, in the prior art hydraulic motors of the type described, small bolts are used frequently in a power transmission train so that the problem of the durability arises. Moreover the rigidity of bolts used for joining between the casing and the valve unit as well as the rigidity of the casing itself present a problem.
Accordingly, one of the objects of the present invention is to overcome the above and other problems encountered in the prior art hydraulic motors of the type described without causing any sacrifice of their desirable features and advantages. The present invention will become apparent from the following description of the preferred embodiments thereof taken in conjunction with the accompanying drawings.